The present invention relates to a method and apparatus for feeding replenishment chemicals in photographic film or paper processors. More particularly, the invention relates to improvements in a method and apparatus for feeding replenishment chemicals in processors wherein webs or strips of exposed photographic film or photographic paper are transported through one or more liquid baths and wherein the speed, width and/or number of transported photosensitive webs varies at regular or irregular intervals and within a narrow or wide range.
Webs of photographic film or photographic paper are treated in developing machines wherein they pass through one or more vessels or tanks containing different liquids, such as a developing bath, a fixing bath and a rinsing bath. In order to compensate for loss in activity, it is necessary to supply the baths with replenishment chemicals, either continuously or intermittently. The chemicals (this term is intended to embrace developing agents, fixing agents as well as any other agents, including water, which are held in storage for admission to the respective baths by resorting to replenishment pumps or other feeding units) should be admitted in dependency on the quantity of material which has passed through the respective tank per unit of time, i.e., in proportion to the surface area of the treated photosensitive material. In certain presently known developing machines wherein one or more webs of photographic film or paper are transported through successive tanks along discrete paths, each path is monitored by a microswitch which transmits or causes the transmission of signals whose intensity or another characteristic is indicative of the quantity of conveyed material. The signals are transmitted to an electric impulse generator which actuates the respective feeding unit whenever the intensity and/or number of signals indicates that the corresponding tank must receive a supply of replenishment chemicals. In most instances, each feeding involves the admission of a predetermined quantity of replenishment chemicals.
The just discussed feeding apparatus exhibit a number of drawbacks, especially as regards the accuracy of maintaining the level of activity of one or more baths within a rather narrow range. This is due to the fact that the conventional apparatus do not take into consideration all factors which influence the activity of the bath or baths. Such factors include the speed of transport of film and/or paper, the width of webs and/or others. On the other hand, it is highly desirable to construct and assemble a developing machine in such a way that it can simultaneously process two or more webs of photographic film or paper, to shift from the processing of a single web to the processing of two or more webs (or vice versa), and/or to treat relatively narrow or relatively wide webs, either simultaneously or one after the other. If the presently known principles of monitoring the webs were applied in such machines, each machine would be equipped with a large number of monitoring devices and with rather complex evaluating circuitry for the signals which are furnished by the monitoring devices.
German Offenlegungsschrift No. 1,522,856 discloses a processor wherein a sensor is moved transversely of the path of a running web in order to determine the width of the transported material. It has been found that mere determination of width does not suffice to insure that the activity of each and every bath remains constant or nearly constant. This will be readily appreciated by considering that successive webs are normally attached to each other by strips consisting of a material which is not photosensitive. Such strips are also used to connect the ends of webs to the cores of supply and takeup reels. The mobile sensor which is disclosed in the German Offenlegungsschrift No. 1,522,856 cannot discriminate between photosensitive and other materials and, therefore, its ability to monitor the width of webs does not contribute significantly to satisfactory feeding of replenishment chemicals. Moreover, the just discussed apparatus does not have any film velocity sensor means for determining the exact length of those portions of webs which are transported through the bath or baths per unit of time.